Coupling a trailer to the hitch on a towing vehicle can be a tricky task. In addition to the physical coupling, the operator must ensure that the loads are distributed properly in both the trailer and the towing vehicle. Beyond that, the coupling between the trailer and towing vehicle must try to keep both loads as level as possible. This keeps the trailer and towing vehicle in the same plane, or parallel planes, and tends to keep the dynamic forces between the trailer and towing vehicle planar or parallel. Such an arrangement promotes safe control.
However, if the towing vehicle is not level, so that the trailer hitch is too high or too low, the trailer can introduce vertical forces into the towing vehicle. This problem is aggravated by a trailer geometry that places the tongue too high or too low, relative to the towing vehicle. Another problem is where the towing vehicle has a high hitch position, such as on a large truck, while the trailer is level only when the tongue is significantly lower than the hitch.
Fortunately for most consumers, most serious hitches are of the square receiver type. A draw bar with a ball mount slides into the receiver and it is pinned in place. Many draw bars are available with a fixed amount of drop, measured from the centerline of the receiver. The drop can be converted into rise if the draw bar is inverted and the ball is removed and installed to the opposite side. This is commonly done to compensate for disparate hitch and trailer tongue heights. The systems discussed above are fixed, that is, the drop or rise is built into the draw bar and cannot be changed. This works for many people with predictable loads and less-demanding towing situations, but is not sufficient for others.
An adjustable-height draw bar is necessary for those who want to have the safest possible towing situation. An adjustable-height draw bar can be adjusted to compensate for the variations that occur each time a trailer is coupled. This can be a big advantage where the tongue weight of the trailer varies considerably depending on its load, or where the towing vehicle has a much larger or smaller load than normal.
Several varieties of adjustable-height draw bars are on the market, but each has drawbacks. Some are adjustable only over a small range or in very large increments. All of them include a zero-elevation dead spot where it is impossible to adjust the center of the tow ball so that it is level with the square receiver. Existing designs require that the operator have a second draw bar to have the tow bal level with the square receiver.
Thus, what is desired is a trailer hitch system that provides quick and easy elevation adjustments of the trailer hitch with a trailer, and that eliminates the zero-elevation dead spot so that an operator needs only one adjustable draw bar for a wide range of elevation adjustments.